Several publications and patent documents are cited throughout this application in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these citations is incorporated by reference herein.
Bovine viral diarrhea virus (BVDV) costs the United States cattle industry more than 400 million dollars per year. The pathogenesis of BVDV infection has features that are unique to this virus and vary with the time of infection, virulence of the viral strain, and age of the animals at the time of infection.
When the infection occurs after 150 days of gestation (post-development of the fetal immune system) or after birth, including adult animals, the infection is referred to as acute infection. The clinical manifestation of acute BVDV infection ranges from sub-clinical or unapparent infections to embryonic death, abortions, increased incidence of stillborn calves, malformed or slow growing calves.
Certain strains of BVDV can cause a hemorrhagic syndrome with high morbidity and moderate mortality in adult animals. Acutely infected animals usually recover and eliminate the virus within 10 to 14 days post infection.
Animals vaccinated with modified live vaccines against BVDV have an immune response similar to the one induced by natural, acute infection. In contrast, infection of the fetus during the first 150 days of gestation, when the fetal immune system has not yet developed, can lead to the generation of persistently infected (PI) calves. Some of these PI calves die soon after birth, but others live for relatively long periods of time without showing any clinical signs. PI animals cannot eliminate the infecting BVDV from their system, and continuously release high amounts of virus in their bodily secretions and excretions, making them a continuous source of infection within the herd and potentially to other herds as well. Furthermore, nursing PI calves can acutely infect their mothers through nasal-respiratory transmission and other normal nursing calves, which, if not vaccinated, in turn infect their own mothers while they are pregnant, producing a new cycle of infection and eventually more PI calves.
Mucosal disease, a fatal complication observed in PI calves, occurs when the virus mutates or the animal is superinfected with an antigenically related BVDV virus. Current vaccines are relatively inefficient in preventing fetal infections, therefore the identification and elimination of PI animals is essential to any successful program for control or eradication of BVDV.
Currently available tests for the detection of PI animals are based on the identification of the viral antigen in a blood or tissue sample (most commonly a skin biopsy) using detection methods that depend on the specific binding of anti-BVDV antibodies. Although these tests are widely used for the detection of PI animals they frequently fail to identify all infected animals (false negatives) resulting in the failure to remove all PI animals from the infected herd. Moreover, serological tests cannot differentiate between PIs and uninfected animals, or between acutely infected and vaccinated animals.
Identification and elimination of PI animals from an infected herd is the most cost effective measure to control and eradicate BVDV, underscoring the criticality of an inexpensive and convenient diagnostic test. The present invention provides such a test and kit for performing the same.